From the Communities and  Local Government website:

The Code measures the sustainability of a new home. It went live in England as a voluntary standard in April 2007. This consultation document follows on from the positive response received to Building a Greener Future: Towards Zero Carbon Development, where we asked if rating against the Code should be mandatory.

Consultation is aimed at Housing development industry, architects, construction companies, planners, energy efficiency specialists, environmental stakeholders and academics.